1. Field of the Invention
The present invention relates to power converters, and more particularly, relates to a synchronous rectifier of switching power converters.
2. Description of the Related Art
FIG. 1 shows a circuit schematic of a soft switching power converter. It includes a transformer 10 to provide isolation from line input VIN to the output VO of the power converter for safety. Switches 20 and 30 develop a half bridge circuit to switch the transformer 10. A leakage inductance of a primary winding NP of the transformer 10 and capacitors 41, 42 form a resonant tank. The inductance L of the leakage inductance and the equivalent capacitance C of capacitors 41, 42 determine the resonance frequency f0 of the resonant tank.
                              f          0                =                  1                      2            ⁢            π            ⁢                                          L                ×                C                                                                        (        1        )            
The transformer 10 transfers the energy from the primary winding NP to the secondary windings NS1 and NS2 of the transformer 10. Rectifiers 61, 62 and a capacitor 65 perform the rectifying and filtering to the transformer 10 for generating a DC voltage VO at the output of the power converter.
Although the soft switching power converter can achieve high efficiency and low EMI (electric-magnetic interference) performance, the forward voltage of rectifiers 61 and 62 still causes significant power losses. The object of present invention is to provide the synchronous rectifying circuit for switching power converter to achieve higher efficiency.